The present invention relates to a semiconductor device, a semiconductor module and a hard disk, and especially to a structure capable of efficiently dissipating heat from a semiconductor chip.
Due to the recent growth of the use of semiconductor devices in portable devices and small/densely-mounted devices, the reduction in size and weight and the improvement in heat dissipation properties are demanded at the same time. In addition, semiconductor devices are mounted on various types of substrates, which, in turn, are mounted in various many systems as semiconductor modules. As for such a substrate, the use of a ceramic substrate, a printed board, a flexible sheet, a metal substrate or a glass substrate etc. may be contemplated, and the following description gives one example thereof. Here, the semiconductor module is explained as being mounted on a flexible sheet.
FIG. 17 shows an example in which a semiconductor module using a flexible sheet is mounted in a hard disk 100. This hard disk 100 may be, for example, the one described in detail in an article of Nikkei Electronics (No. 691, Jun. 16, 1997, p.92-).
This hard disk 100 is accommodated within a casing 101 made of a metal, and comprises a plurality of recording disks 102 that are integrally attached to a spindle motor 103. Over the surfaces of individual recording disks 102, magnetic heads 104 are respectively disposed each with a very small clearance. These magnetic heads 104 are attached at the tips of suspensions 106 which are affixed to the ends of respective arms 105. A magnetic head 104, a suspension 106 and an arm 105 together form one integral body and this integral body is attached to an actuator 107.
the magnetic heads 104 must be electrically connected with a read/write amplifying IC 108 in order to perform read and write operations. Accordingly, a semiconductor module comprising this read/write amplifying IC 108 mounted on a flexible sheet 109 is used, and the wirings provided on this flexible sheet 109 are electrically connected, ultimately, to the magnetic heads 104. This semiconductor module 110 is called xe2x80x9cflexible circuit assemblyxe2x80x9d, typically abbreviated as xe2x80x9cFCAxe2x80x9d.
From the back surface of the casing 101, connectors 111 provided on the semiconductor module 110 are exposed, and these connector (male or female) 111 and connectors (female or male) attached on a main board 112 are engaged. On this main board 112, wirings are provided, and driving ICs for the spindle motor 103, a buffer memory and other ICs for a driving, such as ASIC, are mounted.
The recording disk 102 spins at, for example, 4500 rpm via the spindle motor 103, and the actuator 107 detects the position of the magnetic head 104. Since this spinning mechanism is enclosed by a cover provided over the casing 101, there is no way to completely prevent the accumulation of heat, resulting in the temperature rise in the read/write amplifying IC 108. Therefore, the read/write amplifying IC 108 is attached to the actuator 107 or the casing 101 etc. at a location having a better heat conduction property than elsewhere. Further, since revolutions of the spindle motor 103 tend to high speed such as 5400, 7200 and 10000 rpm, this heat dissipation has more importance.
In order to provide further detail of the FCA explained above, the structure thereof is shown in FIG. 18. FIG. 18A is the plan view, and FIG. 18B is a cross-sectional view taken along the line Axe2x80x94A which cuts across the read/write amplifying IC 108 provided on one end of the module. This FCA 110 is attached to an internal portion of the casing 101 in a folded-state, so that it employs a first flexible sheet 109 have a two-dimensional shape that can easily be folded.
On the left end of this FCA 110, the connectors 111 are attached, forming a first connection section 120. First wirings 121 electrically connected to these connectors 111 are adhered on the first flexible sheet 109, and they extend all the way to the right end. The first wirings 121 are then electrically connected to the read/write amplifying IC 108. Leads 122 of the read/write amplifying IC 108 to be connected to the magnetic heads 104 are connected with second wirings 123 which, in turn, are electrically connected to third wirings 126 on a second flexible sheet 124 provided over the arm 105 and suspension 106. That is, the right end of the first flexible sheet 109 forms a second connection section 127 at which the first flexible sheet 109 is connected to the second flexible sheet 124. Alternatively, the first flexible sheet 109 and the second flexible sheet 124 may be integrally formed. In this case, the second wirings 123 and the third wirings 126 are provided integrally.
On the back surface of the first flexible sheet 109 on which the read/write amplifying IC 108 is to be provided, a supporting member 128 is disposed. As for this supporting member 128, a ceramic substrate or an Al substrate may be used. The read/write amplifying IC 108 is thermally coupled with a metal that is exposed to inside of the casing 101 through this supporting member 128, so that the heat generated in the read/write amplifying IC 108 can be externally released.
With reference to FIG. 18B, a connecting structure between the read/write amplifying IC 108 and the first flexible sheet 109 will now be explained.
This flexible sheet 109 is constituted by laminating, from the bottom, a first polyimide sheet 130 (first PI sheet), a first adhesion layer 131, a conductive pattern 132, a second adhesion layer 133 and a second polyimide sheet 134 (second PI sheet), so that the conductive pattern 132 is sandwiched between the first and second PI sheets 130 and 134.
In order to connect the read/write amplifying IC 108, a portion of the second PI sheet 134 and the second adhesion layer 133 are eliminated at the connection section to form an opening 135 which exposes the conductive pattern 132. The read/write amplifying IC 108 is electrically connected thereto through leads 122 as shown in the figure.
The semiconductor device packaged by an insulating resin 136 as shown in FIG. 18B has heat dissipating paths indicated by arrows for externally dissipating its heat. Especially, since the insulating resin 136 gives the thermal resistance, the semiconductor device has a structure that the heat generated by the read/write amplifying IC 108 cannot be efficiently dissipated to the outside the device.
Further details will now be explained using this example in hard disk application. As for the read/write transfer rate of a hard disk, a frequency of 500 MHz to 1 GHz, or even a greater frequency, is required, so that the read/write speed of the read/write amplifying IC 108 must be fast. To this end, the paths of the wirings on the flexible sheet that are connected to the read/write amplifying IC 108 has to be shorten, and the temperature rise in the read/write amplifying IC 108 must be suppressed.
Especially, since the recording disks 102 are spinning at a high speed, and the casing 101 and the lid provide a molded space, the interior temperature would rise up to around 70 to 80xc2x0 C. On the other hand, a typical allowable temperature for the operation of an IC is approximately 125xc2x0 C. This means that, from the interior temperature of 80xc2x0 C., a further temperature rise by approximately 45xc2x0 C. is permissible for the read/write amplifying IC 108. However, where the thermal resistance of the semiconductor device itself and FCA is large, this allowable operation temperature can easily be exceeded, thereby disabling the device to provide its actual performance level. Accordingly, a semiconductor device and FCA having superior heat dissipating properties are being demanded.
Furthermore, since the operation frequency is expected to further increase in the future, further temperature rise is also expected in the read/write amplifying IC 108 itself due to the heat generated by computing operations. At room temperature, the IC can provide the performance at its intended operation frequency, however, where it is placed inside of a hard disk, its operation frequency has to be reduced in order to restrain the temperature rise.
As described above, further heat dissipating properties of semiconductor device, semiconductor module (FCA) are demanded in connection with the increase of the operation frequency in the future.
On the other hand, the actuator 107, and the arms 105, suspensions 106 and magnetic heads 104 attached thereto has to be designed as light-weighted as possible in order to reduce the moment of inertia. Especially, where the read/write amplifying IC 108 is mounted on the surface of the actuator 107 as shown in FIG. 17, the weight reduction is demanded also for the IC 108 and FCA 110.
The present invention was invented in consideration with the above problems, and in the first aspect, it provides a semiconductor device comprising a semiconductor chip integrally molded with an insulating resin in a face-down state, the semiconductor device having exposed on the back surface thereof a pad electrically connected to a bonding electrode of the semiconductor chip and a heat radiation electrode disposed over the surface of the semiconductor chip, wherein the problem is solved by having the top surface of the heat radiation electrode protrude beyond the top surface of the pad, and practically determining the thickness of a connecting means for connecting the bonding electrode and the pad by the amount of this protrusion.
As for the means to connect the pad and the bonding electrode, an Au bump or a solder ball may be used. The Au bump may comprise at least one stage of an Au cluster, and the thickness thereof would be about 40 xcexcm for a one-stage bump and 70-80 xcexcm for a two-stage bump. Since the height of the heat radiation electrode surface generally matches with the height of the pad surface, the space between the semiconductor chip and the heat radiation electrode is determined by the thickness of the bump. Accordingly, the space between the semiconductor chip and the heat radiation electrode cannot be made any smaller than the thickness of the bump. However, if the surface of the heat radiation electrode is designed to protrude beyond the surface of the pad by the substantial thickness of the bump, the space may be made smaller.
The thickness of a solder bump or a solder ball is approximately 50 to 70 xcexcm, and in this case also, the space may be made small according to the same principle. A brazing material such as solder has a good wettability with the pad, so that when it is in a molten state, it spreads out over the surface of the pad, resulting in a smaller thickness. However, since the gap between the bonding electrode and the pad is determined by the amount of protrusion of the heat radiation electrode, the thickness of the brazing material is determined by this amount of the protrusion. Accordingly, by the amount the brazing material can be made thicker, then the stress applied to the solder bump may be more distributed, so that the deterioration due to heat cycles can be minimized.
In the second aspect, the problem is solved by using an Au bump or a bump of a brazing material such as solder or a solder ball as the connecting means.
In the third aspect, the problem is solved by providing a metal plate on the exposed portion of the heat radiation electrode in a manner so that it protrudes beyond the back surface of the pad.
This protrusive metal plate and the back surface of a flexible sheet which serves as a first supporting member may be made within a same plane, so that a structure is provided, in which the metal plate can be adhered or abutted to the interior of a casing, especially to a member of the casing having a flat surface such as a heat sink plate etc.
In the fourth aspect, the problem is solved by disposing the back surface of the pad and the back surface of the heat radiation electrode substantially within a same plane.
In the fifth aspect, the problem is solved by affixing the semiconductor chip and the heat radiation electrode together by an insulating material.
In the sixth aspect, the problem is solved by affixing the heat radiation electrode and the metal plate together by an insulating material or a conductive material.
In the seventh aspect, the problem is solved by integrally forming the heat radiation electrode and the metal plate from a same material.
In the eighth aspect, the problem is solved by having the back surface of the insulating resin protrude beyond the back surface of the pad.
When forming a brazing material such as solder over the back surface of the pad, the thickness of the solder may be determined by the amount of this protrusion. It also prevents short-circuiting with the conductive pattern extending over the back surface of the semiconductor device.
In the ninth aspect, the problem is solved by having the side surfaces of the pad and the back surface of the insulating resin that extends from the side surfaces of the pad define a same curved surface.
The insulating resin exposed from the back surface of the semiconductor device would define a curved surface when etched, and would exhibit a shape which provides a point contact rather than a face contact. Accordingly, the frictional resistance of the back surface of the semiconductor device is reduced, there by facilitating self-alignment. It also provides a relief for the brazing material which is more effective comparing to a structure in which the protrusive feature of the back surface of the insulating resin is flat. In this way the short-circuiting between the adjacent bumps of the brazing material maybe avoided.
In the tenth aspect, a semiconductor module is provided, which comprises a first supporting member having a conductive pattern provided thereon and a semiconductor device comprising a semiconductor chip which is electrically connected to the conductive pattern and is integrally molded by an insulating resin in a face-down state, the semiconductor device having exposed on the back surface thereof, a pad electrically connected to a bonding electrode of the semiconductor chip and a heat radiation electrode disposed over the surface of the semiconductor chip, wherein the problem is solved by having the top surface of the heat radiation electrode protrude beyond the top surface of the pad, and determining the thickness of a connecting means for connecting the bonding electrode and the pad according to the amount of this protrusion, an by electrically connecting the pad to the conductive pattern provided on the first supporting member, and providing an opening to the first supporting member at a location which corresponds to the heat radiation electrode, the opening accommodating a metal plate which is affixed to the heat radiation electrode.
The distance between the semiconductor chip and the heat radiation electrode can be set so as to assure the conduction of heat, and at the same time, the metal plate thermally coupled with the heat radiation electrode can be abutted to a heat-dissipating substrate provided under the first supporting member.
In the eleventh aspect, the problem is solved by adhering a second supporting member having the metal plate affixed thereto to the back surface of the first supporting member, and affixing this metal plate and the heat radiation electrode together.
In the twelfth aspect, the problem is solved by forming the heat radiation electrode and the metal plate integrally from a same material.
As shown in FIGS. 13 and 14, the metal plate and the heat radiation electrode may be formed integrally by etching a conductive foil, thereby unnecessitating the step for affixing the metal plate.
In the thirteenth aspect, the problem is solved by providing a fixation plate made of a conductive material over the second supporting member at a location which corresponds to the metal plate, and by thermally coupling the fixation plate and the metal plate.
In the fourteenth aspect, the problem is solved by forming, respectively, the metal plate mainly by Cu, the second supporting member mainly by Al, and the fixation plate by a plated film mainly made of Cu formed on the second supporting member.
In this way, the thermal resistance between the second supporting member and the fixation plate may substantially be reduced, so that the temperature rise in the semiconductor chip may be effectively prevented.
In the fifteenth aspect, the problem is solved by having the back surface of the insulating resin protrude beyond the back surface of the pad.
In the sixteenth aspect, the problem is solved by having the side surfaces of the pad and the back surface of the insulating resin which extends from the side surfaces of the pad define the same curved surface.
In the seventeenth aspect, the problem is solved by using the semiconductor chip as a read/write amplifying IC for a hard disk.
In the eighteenth aspect, a semiconductor device is provided, which comprises a semiconductor chip integrally molded by an insulating resin in a face-down state, the semiconductor device having exposed on the back surface thereof, a pad electrically connected to a bonding electrode of the semiconductor chip, an external electrode extending via a wiring integral with the pad, and a heat radiation electrode disposed on the surface of the semiconductor chip, wherein the problem is solved by having the top surface of the heat radiation electrode protrude beyond the top surface of the pad, and determining the thickness of a connecting means for connecting the bonding electrode and the pad practically by the amount of this protrusion.
In the nineteenth aspect, the problem is solved by using an Au bump or a bump made of a brazing material such as solder, or a solder ball.
In the twentieth aspect, the problem is solved by disposing a metal plate over the exposed portion of the heat radiation electrode in a manner so that it protrudes beyond the back surface of the external connection electrode.
In the twenty-first aspect, the problem is solved by disposing the back surface of the external connection electrode and the back surface of the heat radiation electrode substantially within a same plane.
In the twenty-second aspect, the problem is solved by affixing the heat radiation electrode and the metal plate together by an insulating material.
In the twenty-third aspect, the problem is solved by affixing the heat radiation electrode and the metal plate together by an insulating material or a conductive material.
In the twenty-fourth aspect, the problem is solved by integrally forming the heat radiation electrode and the metal plate from a same material.
In the twenty-fifth aspect, the problem is solved by having the back surface of the insulating resin protrude beyond the back surface of the external connection electrode.
In the twenty-sixth aspect, the problem is solved by having the side surfaces of the external connection electrode and the back surface of the insulating material which extends from the side surfaces of the external connection electrode define a same curved surface.
In the twenty-seventh aspect, a semiconductor module is provided, which comprises a first supporting member having a conductive pattern provided thereon, and a semiconductor device including a semiconductor chip which is electrically connected to the conductive pattern and is integrally molded by an insulating resin in a face-down state, the semiconductor device having exposed on the back surface thereof, a pad electrically connected to a bonding electrode of the semiconductor chip, an external connection electrode provided via a wiring integral with the pad and a heat radiation electrode disposed over the surface of the semiconductor chip, wherein the problem is solved by having the top surface of the heat radiation electrode protrude beyond the top surface of the pad, and determining the thickness of a connecting means for connecting the bonding electrode and the pad practically by the amount of this protrusion, and by electrically connecting the conductive pattern provided on the first supporting member and the external connection electrode, and providing an opening in the first supporting member at a location corresponding to the heat radiation electrode, the opening accommodating a metal plate affixed to the heat radiation electrode.
In the twenty-eighth aspect, the problem is solved by adhering a second supporting member having the metal plate affixed thereto onto the back surface of the first supporting member.
In the twenty-ninth aspect, the problem is solved by integrally forming the heat radiation electrode and the metal plate from a same material.
In the thirtieth aspect, the problem is solved by providing a fixation plate made of a conductive material on the second supporting member at a location corresponding to the metal plate, and by thermally coupling the fixation plate and the metal plate.
In the thirty-first aspect, the problem is solved by forming, respectively, the metal plate mainly by Cu, the second supporting member mainly by Al and the fixation plate by a plated film mainly made of Cu formed on the second supporting member.
In the thirty-second aspect, the problem is solved by having the back surface of the insulating adhesive means protrude beyond the back surface of the external connection electrode.
In the thirty-third aspect, the problem is solved by having the side surfaces of the external connection electrode and the insulating adhesive means extending from the side surfaces of the external connection electrode define a same curved surface.
In the thirty-fourth aspect, the problem is solved by using the semiconductor chip as a read/write amplifying IC for a hard disk.